Electron discharge device



Dec. 25, w45. f J. HILUER 2,391,780

`ELECTRON DISCHARGE DEVICE Filed Oct. 13, 1943 2 Sheets-Sheet l SnventorGttcrneg ec. 25, 1945. J. HILLIER ELECTRON DISCHARGE DEVICE 2Sheets-Sheet 2 Filed oet. 13, 1945 :inventor Gttorfleg Patented Dec. 25,1945 ELECTRON DISCHARGE DEVICE James Hillier, Granbury, N. J., assignerto Radio Corporation of America, a corporation of Dela- Ware ApplicationOctober 13, 1943, Seria/l N0. 506,035

(Cl. ,Z50-27.5)

Claims.

This invention relates to electron discharge devices, particularly toimprovements in so-called ray tubes, and has for its principal object toprovide an improved electrode assembly and subassembly for electronmicroscopes and other electron discharge devices wherein the filament orother source of electrons must be aligned with a high degree of accuracywith respect to a reference line or to one or more apertured electrodesor lens elements.

In electron discharge devices of the general character described, andespecially in electron optical instruments wherein an image of highresolution is required, it is customary to employ a point type cathodeas the primary source of electrons. Such cathodes may comprise aneedlelike element, such for example as the one shown in U. S. Patent2,271,990 to Edward G. Ramberg or, more conventionally, a hairpin lamentwherein the bend is not rounded, but pointed. When, as is usually thecase, the cathode is constituted of tungsten, diiiiculties arise inmaintain' ing the point-source in alignment with the grid, anode andlens apertures. This is so principally because of the well knowntendency of tungsten to warp when first subjected to heating currents.It has accordingly been the practice to provide the microscope or otherdevice, in which such cathodes are used, with a flexible couplingintermediate the cathode and lens chambers and to Amove the cathodechamber, in its entirety, with respect to the lens chamber in order toorient and align the electron beam with the apertured electrodes withinthe said chambers. (As to this see U. S. Patent 2,319,061 to the sameinventor.) While such flexible mountings correct for certaininaccuracies of alignment they cannot correct for those due todecentering of the iilament relative to the other parts of the cathode.Moreover, such flexible mountings and adjusting means complicate theconstruction and contribnte materially to the cost of the instrument.

Accordingly, another and important object of the present invention is toprovide a simple, inexpensive and trouble-free adjustable electrodeassembly, and one which may be adjusted without resorting to the use offlexible couplings and other more or less complicated auxiliary devices.

Certain preferred details o-f construction together with other objectsand advantages will be apparent and the invention itself will be bestunderstood by a reference to the following speciiication and to theaccompanying drawings, wherein Figure 1 Ais a sectional elevational viewof the cathode chamber of an electron microscope showing a removableadjustable electrode assembly constructed in accordance with oneembodiment of the invention.

Figure 2 is a horizontal sectional view a line II-II of Figure 1,

Figure 3 is a fragmentary sectional view, rotated of the cathode-gridassembly shown in Figure 1,

.Figures 4 and 5 are Ahorizontal sectional views, respectively, on thelines IV-IV, V-V of Figure 1.

In the accompanying drawings wherein like reference characters designatethe same parts in all gures, I designates an end wall and 3 the sidewall of a cylindrical casing surrounding the cathode chamber 5 of anelectron microscope orl other cathode ray device. The end wall vI isprovided with a centrally located aperture 1 through which a glass orother insulating conduit B extends. This conduit contains two cathodeleads I I, Ila and a Athird lead, I3. As shown Yin Figure l, the conduit9 is of a reduced diameter adjacent to its leading end and cathode leadsII, I Ia are xed thereto as by bending them over the said end. Acircular ange 9a, a complementarily shaped seat I5 for the said iiange,and a gasket I1 and clamping ring I9 on the end wall I of the casingserve as a vacuum-tight support for the conduit 9. The side wall 3 ofthe casing I contains one or more apertures 2l through taken on whichaccess may be had to the interior of the cathode chamber when avacuum-tight door 23 is opened.

Referring particularly to Figs. 1 and 2, an insulator in the form of anannulus 25 is held within the chamber l adjacent to the end wall I bymeans of a clamp, not shown but which will be understood to be soarranged vat the opposite end of the chamber that it exerts its forceupon the saidinsulator through an anode structure 21, and a cylindricalspacer 29 which has ka sliding .fit within the bore of the outercylinder 3. Ordinarily the anode 21 and the outer casing 3 aremaintained at ground potential and the cathode and cathode focusingelectrode at potentials of the order of 30 kilovolts negative withrespect to ground. Accordingly, in order to prevent corona dischargebetween the leads II, Ila and 'I3 and the grounded casing I, 3 kit ispreferable to provide the insulator `25 with a ribbed or other extendedsurface 25a and having a central depression 25h which accommodates aconical corona shield 3l within which the end of the conduit 9 isreceived.

of its support 33.

I'he central portion of the inner surface of the insulator 25 serves asa support for a circular metal shell or box 33 which has an opening 33a(see Fig. 4) in its side wall in register with one of the vacuum-tightdoors 23 so that a capsule 35 containing an adjustable cathode assembly(later described) may be entered therein. It Will be observed uponinspection of Figs. 2 and 3 that the metal box or support 33 A#isconnected to the lead I3 by means of a leaf spring 31 which is biased tobear against the end of the said lead I3. It will also be observed thatthe box 33 is provided with a circular aperture at the center of itsbottom surface and that this aperture serves as a seat for a similarlyshaped apertured protuberance 35a on the bottom of the capsule 35 whichcontains the cathode assembly. This protuberance 35a and the cupshape-portion 35h of the capsule from which the part 35a protrudes maybe said to comprise the grid of the device. The conductive supportingshell 33 in which the said grid is mounted is sufficiently rigid and isso carefully'oriented with respect to the long (vertical) axis of thechamber 5 that when the protuberance 35a is seated within the shell thegrid aperture 35c will be in perfect alignment with the aperture 21a inthe anode 21.

As previously indicated, the removable capsule 35 serves not only as agrid, or focusing electrode,

but also as a container for the filament 39 of the device and for anadjusting mechanism (later described) for orienting the filament withrespect to the grid aperture 35c. Since the seating of the gridprotuberance 35a within the shell 33 brings the grid aperture 35c intoalignment with the anode aperture 21a (Fig. 1) it will be apparent thatlwhen the filament 39 is properly aligned with the grid aperture 35c itis also in alignment with the aperture 21a in the anode.

Referring now in detail to the adjustable support for the filament 39,as shown more clearly in Figs. 1 and 3, the apertured cup-shape base 35hoi' the capsule 35 is provided with an inverted cup-shape cover 35dwhich fits over the said base and is secured to the side wall thereof asby screws 35e (Figs. 1 and 5). The inner surface of the cover 35d is cutaway adjacent to the top of the lower cup 35h to provide a retaininggroove for a circular insulating plate 4| which is freely mounted formovement on and about the rim of the said lower cup under control ofthree or more screws 43, 43a, etc. (see Fig. 4), which extend throughthe side wall of the capsule 35. The lilament 39 is supported at itsopposite ends by two parallelly arranged screws 45, 45a which extendthrough the movable insulating plate 4| and through a relatively largeopening of the lid or cover 35d of the capsule 35. Insulating grommets41 and 41a surround these screws throughout the greater -portion oftheir length. The ends of the screws, however, are exposed in line withtwo leaf springs 49 and 49a, respectively, through which contact is madewith the filament leads I and Ila, respectively.

It will now be apparent from an inspection of Figs. 1 and 3 that thecapsule 35 may be removed from the chamber 5 through the port 2| by rstlifting it (against the biasing force of the leaf springs 49, 49a and31) from its seat in the base To mount a new filament Within the capsule35 the screw or screws 35e are unscrewed from the side wall of thecapsule; the cover 35d is then removed and the insulating plate togetherwith the filament supporting screws 45, 45a and grommets 41, 41a arelifted screws and springs shown in the drawings.

from the rim of the bottom cup 35a, whereupon the old filament may beremoved and a new lament mounted in place by inserting its opposite endsin the heads of the parallelly arranged supporting screws 45, 45a.

If, instead of the fllamentary cathode here shown, a needle-like cathode(e. g. similar to the one shown in U. S. Patent 2,271,990 to Ramberg) isemployed as the point source of electrons, a single centrally locatedsupporting screw and contact spring can be substituted for the paired Ineither event, when the cathode and its supporting plate 4| are mountedwithin the capsule and the cover 35d screwed on, the cathode may bepermanently aligned with the aperture 35c in the base 35a of the capsulein the following manner: The point or apex of tho cathode is first moreor less accurately aligned within the closed capsule by means of thefour adjusting screws 43, 43a, 43h, 43e which control the movement ofthe insulating plate upon which the cathode is supported. The capsule isentered through the port 2|, and seated in the shell 33, then the dooris closed and the chamber 5 evacuated. The cathode is then energized,preferably at its normal operating current, for a p eriod sufilcientlylong for the cathode to assume its ultimate shape. When the cathode isconstituted of tungsten, a pre-heating period of about thirty secondswill usually suilice. The vacuum is then broken, the capsule removed andthe cathode realigned in the same manner as before, i. e., laterally, bymeans of the adjusting screws 43, 43a, etc. and without removing thecover 35d and Ipreferably without jarring the capsule. The adjustmentmay be observed, preferably with the aid of a magnifying glass, throughthe aperture 35c in the base of the capsule. When the point or apex ofthe cathode is aligned with the desired high degree of accuracy withrespect to the grid aperture 35c the capsule is re-inserted in itssupporting shell or box 33 .Within the cathode chamber 5. As previouslyset forth, the box 33 is so rigid and so carefully mounted with respectto the central axis of the chamber 5 that when the protuberance 35a onthe bottom of the capsule is seated on the base of the box the gridaperture 35c is in perfect alignment with the aperture 21a in the anode21.

What is claimed is:

l. The combination with an electron dlscharge device comprising anevacuable chamber containing an apertured anode, a port in a wall ofsaid chamber, a rigid support for an electrode sub-assembly mountedwithin said chamber and accessible from said port, an electrodesub-assembly comprising a capsule having an aperture therein and adaptedto be passed through said port and seated within said support with saidaperture in register with the aperture in said apertured anode, anelectron source mounted to permit lateral movement within said capsule,and means for moving said electron source laterally within said capsulewith respect to said registered capsule and anode apertures.

2. An electrode sub-assembly for an electron discharge device having anevacuable envelope, said sub-assembly comprisinga capsule having anaperture therein and adapted to be received within said evacuableenvelope, an electron source mounted to permit lateral movement withinsaid capsule, and means accessible from the exterior of said capsule formoving said electron source laterally within said capsule and withrespect to said aperture.

3. The invention as set forth in claim 2 and wherein said capsule isconstituted of metal and said source of electrons is insulatinglysupported within said metal capsule, whereby said capsule and saidelectron source may be separately energized.

4. The invention as set forth in claim 2 and wherein the mount for saidelectron source comprises an insulating member supported for movementlin al1 directions in a plane normal to the axis of said aperture.

5. An electrode sub-assembly comprising a capsule comprising a cup-shapemetal base having a centrally located aperture in the bottom thereof, asimilarly shaped cover Within which said base is adapted to be fitted,the rim of said cup-shape base and the adjacent portion of ysait! coverbeing cut away to provide a circular groove on the interior of saidcapsule, a circular insulating plate of a diameter smaller than that ofsaid circular groove supported upon said rim Within said groove formovement in all directions in the plane of said rim, a point-source ofelectrons supported on said insulating plate on the side thereof facingthe said aperture, and a plurality of adjusting members spaced apartabout said circular groove and extending radially outwardly to theexterior of said cover` for orienting said insulating plate and hencesaid point source of electrons with respect to said aperture.

JAMES HILLIER..

